CN107799650B

CN107799650B - Ferroelectric heterojunction and preparation method thereof and electronic control microwave electronic component

Info

Publication number: CN107799650B
Application number: CN201711079721.6A
Authority: CN
Inventors: 代波; 李俊; 任勇
Original assignee: Southwest University of Science and Technology
Current assignee: Southwest University of Science and Technology
Priority date: 2017-11-06
Filing date: 2017-11-06
Publication date: 2020-06-02
Anticipated expiration: 2037-11-06
Also published as: CN107799650A

Abstract

The invention provides a ferroelectric heterojunction, a preparation method thereof, and an electronically controlled microwave electronic component. The ferroelectric heterojunction includes an electrode layer, a piezoelectric substrate layer, a buffer layer, an exchange-biased multilayer film, and a protective layer in sequential contact, wherein the exchange-biased multilayer film is [ferromagnetic layer/anti-iron] Magnetic layer] _N , where N is the number of periods, and N≥2, the ferromagnetic layer is a ferromagnetic material with a small magnetostriction coefficient. The invention can provide a new type of ferroelectric heterojunction containing ferromagnetic/antiferromagnetic exchange bias multilayer films; and can also adjust the high-frequency performance of the magnetic thin film with a small magnetostriction coefficient in a wide range, thereby obtaining Ferroelectric heterojunction with good high frequency magnetic properties. The ferroelectric heterojunction of the present invention has a wide range of uses, for example, it can be used in a new generation of electronically controlled microwave electronic components.

Description

Ferroelectric heterojunction and preparation method thereof and electronic control microwave electronic component

Technical Field

The invention belongs to the technical field of magnetic materials and manufacturing thereof, and particularly relates to a ferroelectric heterojunction containing a ferromagnetic/antiferromagnetic exchange bias multilayer film, a preparation method thereof and an electronic control microwave electronic component containing the ferroelectric heterojunction.

Background

At present, research on multiferroic heterojunctions mostly focuses on regulating and controlling static magnetism of magnetic materials through stress conduction, such as 180-degree turning of magnetic domains by pressurization, regulation and control of anisotropic magnetoresistance of materials and the like.

However, the inventors have not found studies on high-frequency magnetic properties of a multilayer film having a small magnetostriction coefficient. Magnetic films with smaller magnetostriction coefficients, such as CoFe, NiFe, CoFeB and the like, also have wide application in high-frequency magnetic properties.

Disclosure of Invention

The present invention aims to address at least one of the above-mentioned deficiencies of the prior art.

For example, it is an object of the present invention to provide a novel ferroelectric heterojunction including a ferromagnetic/antiferromagnetic exchange-biased multilayer film and a method for manufacturing the same.

An aspect of the present invention provides a ferroelectric heterojunction. The ferroelectric heterojunction comprises an electrode layer, a piezoelectric substrate layer, a buffer layer, an exchange bias multilayer film and a protective layer which are sequentially contacted, wherein the exchange bias multilayer film is a ferromagnetic layer/an anti-ferromagnetic layer]_NN is the number of cycles, and N is more than or equal to 2.

In an exemplary embodiment of the present invention, the buffer layer may have a thickness of 1 to 100nm, the ferromagnetic layer may have a thickness of 5 to 100nm, the antiferromagnetic layer may have a thickness of 3 to 100nm, and the protective layer may have a thickness of 1 to 100 nm. Both ranges are inclusive of the two endpoints.

In one exemplary embodiment of the invention, the ferromagnetic layer may be Co, Fe, Co_xFe_1-x、Ni_yFe_1-yAny one of CoFeB and FeSi, wherein, 0.5<x<0.95，0.65<y<0.90。

In one exemplary embodiment of the present invention, the ferroelectric heterojunction may further include another electrode layer formed on a side of the protective layer not combined with the exchange-biased multilayer film.

Another aspect of the invention provides a method of making a ferroelectric heterojunction. The method comprises the following steps: forming a buffer layer on a first surface of the piezoelectric substrate layer; growing an exchange-biased multilayer film on the buffer layer, wherein the exchange-biased multilayer film is a [ ferromagnetic layer/antiferromagnetic layer ]]_NN is the number of cycles, and N is more than or equal to 2; forming a protective layer on the exchange-biased multilayer film; and forming an electrode layer on a second surface of the piezoelectric substrate layer to obtain the ferroelectric heterojunction, wherein the second surface is opposite to the first surface.

In one exemplary embodiment of the present invention, the method may further include the step of applying a voltage between the electrode layer (bottom electrode) and the protective layer or another electrode layer (top electrode), and then removing the voltage.

In an exemplary embodiment of the present invention, the intensity of the voltage may be 100 to 2000V.

Both ranges are inclusive of the two endpoints. The ferromagnetic layer may be Co, Fe, Co_xFe_1-x、Ni_yFe_1-yAny one of CoFeB and FeSi, wherein, 0.5<x<0.95，0.65<y<0.90。

The invention also provides an electric control microwave electronic component. The electric control microwave electronic component comprises the ferroelectric heterojunction prepared by the method for preparing the ferroelectric heterojunction.

Compared with the prior art, the invention has the beneficial effects that: a novel ferroelectric heterojunction can be provided comprising a ferromagnetic/antiferromagnetic exchange-biased multilayer film. In addition, the invention can also adjust the high-frequency performance of the magnetic film with smaller magnetostriction coefficient in a large range, thereby obtaining the good high-frequency magnetic ferroelectric heterojunction. The ferroelectric heterojunction of the present invention has a wide range of applications, for example, it can be used for a new generation of electrically controlled microwave electronic components.

Drawings

Figure 1 shows a schematic structural diagram of a ferroelectric heterojunction according to an exemplary embodiment of the present invention;

fig. 2 shows a graph of deformation versus voltage (S-E curve) for a ferroelectric heterojunction sample according to an exemplary embodiment of the present invention;

FIG. 3 shows static magnetic contrast curves of a ferroelectric heterojunction sample before and after voltage application according to an exemplary embodiment of the present invention, wherein the ordinate represents normalized magnetization (M/Ms/(a.u.)) and the abscissa represents the magnitude of applied magnetic field (H/Oe);

fig. 4 shows high frequency magnetic contrast curves of a ferroelectric heterojunction sample before and after application of a voltage according to an exemplary embodiment of the present invention.

Detailed Description

Hereinafter, the ferroelectric heterojunction, the method of manufacturing the same, and the electrically controlled microwave electronic component of the present invention will be described in detail with reference to exemplary embodiments.

In one exemplary embodiment of the present invention, the ferroelectric heterojunction may include an electrode layer, a piezoelectric substrate layer, a buffer layer, an exchange-biased multilayer film, and a protective layer in sequential contact, wherein the exchange-biased multilayer film is a [ ferromagnetic layer/antiferromagnetic layer ]]_NN is the number of cycles, and N is more than or equal to 2. For example, the ferroelectric heterojunction can have a structure of first electrode/piezoelectric substrate/buffer layer/[ ferromagnetic layer/antiferromagnetic layer ]]_NProtective layer.

The electrode or electrode layer may be made of a material having good conductivity, such as Au, Ag, or Pt, and the electrode layer may be referred to as a bottom electrode. However, the present invention is not limited thereto, and other materials with good conductivity may be used as the electrode or the electrode layer of the present invention.

The piezoelectric substrate or piezoelectric substrate layer can be selected from PMN-PT, PZN-PT, SrTiO₃、BaTiO₃The piezoelectric substrate layer of the present invention may be made of any piezoelectric material having stable properties, but the present invention is not limited thereto.

The buffer layer may be formed of a conductive material. For example, the buffer layer may be a conductive material such as Ta, Cu, Cr, or the like. Preferably, the buffer layer may be selected to be of a material that facilitates crystallization of the ferromagnetic layer. The thickness of the buffer layer can be between 1 nm and 100 nm. Here, if the buffer layer is too thin (e.g., thinner than 5nm), an effect of inducing crystallization of the ferromagnetic layer is not exerted; if the buffer layer is too thick (e.g., thicker than 100nm), the magnetic properties of the ferromagnetic layer may be affected.

The exchange-biased multilayer film is formed of a plurality of magnetic layer pairs, each of which may be composed of one ferromagnetic layer and one antiferromagnetic layer.

Wherein the ferromagnetic layer has a small magnetostriction coefficient (e.g., an absolute value of the magnetostriction coefficient is less than 1.6x 10)^-6) Is formed of the ferromagnetic material of (1). For example, the ferromagnetic layer can be made of Co, Fe, Co_xFe_1-x(0.5<x<0.95)、Ni_yFe_1-y(0.65<y<0.90), CoFeB, FeSi, and the like. For example, the thickness of the ferromagnetic layer can be between 5 and 100 nm. Here, if the ferromagnetic layer thickness is too thin (e.g.,thinner than 5nm), the film coercive force is too large, and the application is not facilitated; if the film is too thick (e.g., thicker than 100nm), it is not conducive to the tuning of the underlying ferroelectric substrate.

The antiferromagnetic layer may be formed of an antiferromagnetic material. For example, the antiferromagnetic layer may be selected from Fe_xMn_1-x(0.4<x<0.6)、Ni_xMn_1-x(0.4<x<0.6)、Pt_xMn_1-x(0.4<x<0.6)、Ir_xMn_1-x(0.15<x<0.35), NiO, and the like. For example, the thickness of the antiferromagnetic layer can be between 3 and 100 nm. Here, if the antiferromagnetic layer is too thin (e.g., thinner than 3nm), the pinning effect is lost, resulting in zero exchange bias field; if the film is too thick (e.g., thicker than 100nm), it is also detrimental to the tuning of the underlying ferroelectric substrate.

The protective layer may be formed of a conductive material having an oxidation preventing effect. In addition, the protective layer may also function as a protective layer and may also be used as an electrode on the top layer. For example, the protective layer may be made of a material having a good oxidation preventing effect, such as Ta, Cu, Cr, or Au. For example, the thickness of the protective layer may be 1 to 100 nm. In addition, the ferroelectric heterojunction can also include another electrode layer formed on the side of the protective layer not bonded to the exchange-biased multilayer film, which can be referred to as a top layer electrode.

Fig. 1 shows a schematic structural diagram of a ferroelectric heterojunction according to an exemplary embodiment of the present invention. As shown in FIG. 1, in one exemplary embodiment of the present invention, the ferroelectric heterojunction may be structured by sequentially contacting a first electrode layer (Au), a piezoelectric substrate layer (e.g., 0.7Pb (Mg)_1/3Nb_2/3)O₃-0.3PbTiO₃Denoted as PMN-PT), a buffer layer (Ta), an exchange-biased multilayer film, and a protective layer (Ta). Wherein the exchange-biased multilayer film is composed of two periodically-cycled magnetic layer pairs, each magnetic layer pair being composed of NiFe as a ferromagnetic layer and FeMn as an antiferromagnetic layer.

In another exemplary embodiment of the present invention, a method of fabricating a ferroelectric heterojunction may be achieved by:

(1) forming a buffer layer

Specifically, the buffer layer is formed on a first surface (e.g., a top surface) of the piezoelectric substrate layer. Here, the buffer layer may be formed of a conductive material. For example, the buffer layer may be a conductive material such as Ta, Cu, Cr, or the like. Preferably, the buffer layer may be selected to be of a material that facilitates crystallization of the ferromagnetic layer. The thickness of the buffer layer can be between 1 nm and 100 nm. The piezoelectric substrate layer can be made of PMN-PT, PZN-PT, SrTiO₃、BaTiO₃The piezoelectric substrate layer of the present invention may be formed of any piezoelectric material having stable properties, but the present invention is not limited thereto.

(2) Forming exchange-biased multilayer films

Specifically, an exchange bias multilayer film is grown on the buffer layer formed in the step (1). For example, the exchange bias multilayer film can be grown on the buffer layer by means of direct current magnetron sputtering under room temperature conditions. The exchange-biased multilayer film being a [ ferromagnetic layer/antiferromagnetic layer ]]_NN is the number of cycles, and N is more than or equal to 2. That is, the exchange-biased multilayer film is formed by stacking ferromagnetic layers/antiferromagnetic layers one upon another, and the middle ferromagnetic layer is subjected to the pinning action of the upper and lower antiferromagnetic layers adjacent to the middle ferromagnetic layer. That is, the exchange-biased multilayer film is formed by periodically bonding a plurality of magnetic layer pairs to each other, each of which may be composed of one ferromagnetic layer and one antiferromagnetic layer, with a pinning action between the ferromagnetic layer and the antiferromagnetic layer adjacent to each other or between the antiferromagnetic layer and the ferromagnetic layer adjacent to each other. The exchange-biased multilayer film is bonded to the buffer layer through its outermost (e.g., the lowermost layer of the exchange-biased multilayer film in fig. 1) ferromagnetic layer.

Here, the ferromagnetic layer may be made of a material having a small magnetostriction coefficient (e.g., an absolute value of the magnetostriction coefficient is less than 1.6x 10)^-6) Is formed of the ferromagnetic material of (1). For example, the ferromagnetic layer can be made of Co, Fe, Co_xFe_1-x(0.5<x<0.95)、Ni_yFe_1-y(0.65<y<0.90), CoFeB, FeSi, and the like. For example, the thickness of the ferromagnetic layer can be between 5 and 100 nm. The antiferromagnetic layer may be made of antiferromagneticA magnetic material is formed. For example, the antiferromagnetic layer may be selected from Fe_xMn_1-x(0.4<x<0.6)、Ni_xMn_1-x(0.4<x<0.6)、Pt_xMn_1-x(0.4<x<0.6)、Ir_xMn_1-x(0.15<x<0.35), NiO, and the like. For example, the thickness of the antiferromagnetic layer can be between 3 and 100 nm.

(3) Forming a protective layer

Specifically, a protective layer is formed on the exchange-bias multilayer film formed in the step (2). The protective layer is bonded to the antiferromagnetic layer at the outermost side of the exchange-biased multilayer film (e.g., the topmost layer of the exchange-biased multilayer film in fig. 1). The protective layer may be formed of a conductive material having an oxidation preventing effect. In addition, the protective layer may also function as a protective layer and may also be used as an electrode on the top layer. For example, the protective layer may be made of a material having a good oxidation preventing effect, such as Ta, Cu, Cr, or Au. For example, the thickness of the protective layer may be 1 to 100 nm.

(4) Forming an electrode layer

An electrode layer is formed on a second surface (e.g., bottom surface) of the piezoelectric substrate layer to obtain a ferroelectric heterojunction. The electrode layer may be made of a material having good conductivity, such as Au, Ag, or Pt. However, the present invention is not limited thereto, and other materials with good conductivity may be used as the electrode or the electrode layer of the present invention.

In another exemplary embodiment of the present invention, the method of preparing a ferroelectric heterojunction, in the case of including the above-described steps (1) to (4), may further include a step of applying a voltage between the electrode layer and the protective layer as another electrode and then removing the voltage. The intensity of the voltage can be controlled within the substrate bearing range, for example, the intensity of the voltage can be selected within the range of 100-2000V. Here, if the voltage is too low (e.g., below 100V), the experimental results are not significantly changed; if the voltage is too high (e.g., above 2000V), the substrate may be unacceptable and fragile.

An exemplary embodiment of the present invention is described below in conjunction with a specific example.

Under the condition of room temperature, NiFe/FeMn exchange bias is carried out by direct current magnetron sputtering0.7Pb (Mg) with Ta protective film grown in (011) orientation on multilayer film_1/3Nb_2/3)O₃-0.3PbTiO₃(PMN-PT) on a single-crystal substrate to form PMN-PT/Ta (5nm)/[ Ni ]_0.8Fe_0.2(15nm)Fe_0.5Mn_0.5(6nm)]₂A ferroelectric heterojunction of a/Ta (5nm) multilayer film. The bottom layer of Ta is used as a buffer layer, and the top layer of Ta is used as a protective layer and also used as an electrode of the top layer. Then, 80nm Au was grown on the other side of the PMN-PT as the bottom electrode to form Au/PMN-PT/Ta (5nm)/[ Ni_0.8Fe_0.2(15nm)Fe_0.5Mn_0.5(6nm)]₂a/Ta (5nm) ferroelectric heterojunction. The size of the PMN-PT substrate was 5mm 100]×10mm[01-1]×0.5mm[011]. The tool for applying the voltage was a Keithley 2410 voltmeter; the static magnetism test uses a vibrating sample magnetometer; the high frequency magnetic test tool is a vector network analyzer.

Using the above Au/PMN-PT/Ta (5nm)/[ Ni ]_0.8Fe_0.2(15nm)Fe_0.5Mn_0.5(6nm)]₂Taking a/Ta (5nm) ferroelectric heterojunction as a sample, testing the static magnetism and high-frequency performance of the sample, applying a voltage of +500V on the sample, and slowly removing the voltage (a little reduction every 10V) until the voltage reaches 0V. Then taking out the sample, testing static magnetism and high-frequency performance, comparing the magnetic change before and after pressing, and obtaining the conclusion. All the above experiments can be performed at room temperature.

After analyzing the experimental results, the inventors found that Au/PMN-PT/Ta (5nm)/[ Ni ] containing a bi-periodic exchange bias structure_0.8Fe_0.2(15nm)Fe_0.5Mn_0.5(6nm)]₂the/Ta (5nm) ferroelectric heterojunction shows a great improvement in high-frequency magnetic properties (as shown in FIG. 4) after a +500V voltage is applied, although the static magnetic properties still do not show a great change (as shown in FIG. 3). The inventor analyzes that the middle NiFe layer is pinned by two FeMn layers because of the double-period exchange bias structure, thereby showing higher resonance frequency. After pressurization, the second peak position becomes further away, indicating that its resonant frequency is greatly increased, approximately 0.8 GHz. This kind of fruitThe experimental phenomenon is repeated in a plurality of experiments of the inventor and is a repeatable experimental result. For example, the sample structure can be replaced by PMN-PT/Cu (5nm)/[ Ni ]_0.75Fe_0.25(20nm)Ir_0.2Mn_0.8(10nm)]₃[ Ta (5nm) ]or PMN-PT/Cr (10nm)/[ Fe (25nm) Ir_0.25Mn_0.75(40nm)]₅[ FeCo (15nm) Ir ]/Ta (5nm) or PZN-PT/Ta (10nm)/[_0.25Mn_0.75(20nm)]₅Perta (10nm), or BaTiO₃/Cr(10nm)/[Ni₈₁Fe₁₉(20nm)Ir_0.25Mn_0.75(70n m)]₅Various structures such as/Ta (5 nm).

In summary, the method of the present invention can grow a ferromagnetic/antiferromagnetic exchange bias multilayer film on a piezoelectric material substrate, then apply a voltage, and utilize the deformation of the piezoelectric material after receiving the voltage to induce the exchange coupling effect change between the exchange bias multilayer films, so as to adjust the high frequency performance of the magnetic thin film with a small magnetostriction coefficient in a large range, and further obtain good high frequency magnetism (for example, the resonance frequency can be increased by 0.8 GHz). The ferroelectric heterojunction of the invention has wide application, for example, can be used for the electronic control microwave electronic components of the new generation.

Although the present invention has been described above in connection with the exemplary embodiments and the accompanying drawings, it will be apparent to those of ordinary skill in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A ferroelectric heterojunction, characterized in that the ferroelectric heterojunction comprises an electrode layer, a piezoelectric substrate layer, a buffer layer, an exchange bias multilayer film and a protective layer in sequential contact, wherein the The exchange-biased multilayer film is [ferromagnetic layer/antiferromagnetic layer] _N , N is the number of periods, and N≥2, the exchange-biased multilayer film is composed of a plurality of magnetic layer pairs periodically combined with each other, wherein Each pair of magnetic layers consists of a ferromagnetic layer and an antiferromagnetic layer, and there are nails between the ferromagnetic layer and the antiferromagnetic layer adjacent to each other, or the antiferromagnetic layer and the ferromagnetic layer adjacent to each other tie effect.

2 . The ferroelectric heterojunction according to claim 1 , wherein the thickness of the buffer layer is between 1 and 100 nm, the thickness of the ferromagnetic layer is between 5 and 100 nm, and the thickness of the anti-ferrous layer is between 5 and 100 nm. 3 . The thickness of the magnetic layer is between 3 and 100 nm, and the thickness of the protective layer is between 1 and 100 nm.

3. The ferroelectric heterojunction according to claim 1, wherein the ferromagnetic layer is any one of Co, Fe, CoxFe1 _-x _, NiyFe1 _-y _, CoFeB and FeSi species, where 0.5<x<0.95, 0.65<y<0.90.

4 . The ferroelectric heterojunction according to claim 1 , wherein the ferroelectric heterojunction further comprises another electrode layer formed on the side of the protective layer not combined with the exchange bias multilayer film. 5 .

5. A method for preparing a ferroelectric heterojunction, wherein the method comprises the following steps:

forming a buffer layer on the first surface of the piezoelectric base layer;

An exchange-biased multilayer film is grown on the buffer layer, and the exchange-biased multilayer film is [ferromagnetic layer/antiferromagnetic layer] _N , N is the number of cycles, and N≥2, the exchange bias is more The layer film is composed of a plurality of magnetic layer pairs periodically combined with each other, each of which is composed of a ferromagnetic layer and an antiferromagnetic layer, and the adjacent ferromagnetic layers and antiferromagnetic layers, Or there is a pinning effect between the antiferromagnetic layer and the ferromagnetic layer adjacent to each other;

forming a protective layer on the exchange-biased multilayer film;

The ferroelectric heterojunction is obtained by forming an electrode layer on a second surface of the piezoelectric base layer, wherein the second surface is opposite to the first surface.

6 . The method for preparing a ferroelectric heterojunction according to claim 5 , wherein the method further comprises the steps of applying a voltage between the electrode layer and the protective layer, and then removing the voltage. 7 .

7 . The method for preparing a ferroelectric heterojunction according to claim 6 , wherein the intensity of the voltage is 100-2000V. 8 .

8 . The method for preparing a ferroelectric heterojunction according to claim 5 , wherein the thickness of the buffer layer is between 1 and 100 nm, and the thickness of the ferromagnetic layer is between 5 and 100 nm. 9 . The thickness of the antiferromagnetic layer is between 3 and 100 nm, and the thickness of the protective layer is between 1 and 100 nm.

9. The method for preparing a ferroelectric heterojunction according to claim 5, wherein the ferromagnetic layer is in Co, Fe, Co _x Fe _1-x , Ni _y Fe _1-y , CoFeB and FeSi Any of , where 0.5<x<0.95, 0.65<y<0.90.

10. An electronically controlled microwave electronic component, characterized in that the electronically controlled microwave electronic component comprises a ferroelectric prepared by the method for preparing a ferroelectric heterojunction according to any one of claims 5 to 9 Heterojunction.